The present invention relates to a wind power generation system which realizes to absorb an excessive current generated on a rotor of an AC excitation generator to protect a converter connected to the rotor when occurring a voltage descent caused by a power failure in an electric power system and restart the operation of converter connected to the rotor after absorbing the excessive current without electrically decoupling the wind power generation system from the power system.
The AC excitation generator for use in generating equipment excites a rotor winding in the AC by a slip frequency (a difference between system frequency and rotation frequency) in an electric power converter. Therefore, a voltage generated on a stator side can be made to the same frequency equivalent to the system frequency by the excitation of rotor. That is, an excitation frequency (slip frequency) of the rotor is made variable, in consequence, there is an advantage that the rotation number of a windmill can be made variable and the capacity of power converter can be made small compared with the capacity of generator.
However, the AC excitation generator is intended to supply a current to a fault point in its operation when the voltage descent caused by a grounding fault occurs in the power system. At this time, the excessive current is induced on the rotor winding to thereby flow the excessive current into the excitation converter connected to the rotor side. Therefore, such a method of installing equipment, which shunts a rotor circuit referred to as a Crowbar, has been used.
A specification has been established in Europe in such that the operation must be continued without electrically decoupling the wind power generation system from the power system, at a time of the power system failure. That is, the operation has been demanded in such that an adverse effect on the power system is made small by restarting the generating operation after the failure without electrically decoupling the wind power generation system from the power system at the time of voltage descent in a short time period.
In the past, U.S. Pat. No. 6,921,985 has disclosed a system in which a shunt circuit is made operated when detecting an excessive current of a generator-sided inverter. Further, U.S. Pat. No. 7,321,221 has disclosed a system in which the shunt circuit is made operated when detecting the system voltage descent.